Station selecting device having improved noise discrimination circuitry

Abstract

A multi-channel communication system including automatic station selecting circuitry and circuitry for preventing actuation of the station selection circuitry by noise or the like. The station selecting circuitry automatically, sequentially generates a plurality of local oscillator signals which are mixed with incoming information signals transmitted in one or more of the channels of the system. Whenever the frequency difference between an information signal and a local oscillator signal falls within the pass band of the receiving channel, a sensing signal is generated which stops the automatic station selector so that communications can occur on the selected channel. Circuitry is also employed to discriminate between noise and an appropriate information signal in the receiving channel so that the above-mentioned sensing signals are generated only when information signals are present.

What is claimed is: 
     
       1. A multichannel communication system having a station selecting device, said station selecting device comprising information signal receiving means for receiving information signals over at least one of a plurality of channels;   means for generating a train of first pulses of predetermined width and period;   first signal generating means responsive to said train of first pulses for automatically, sequentially generating a plurality of first signals respectively corresponding to the information signals of said plurality of channels of said information signal receiving means;   said information signal receiving means including means responsive to said plurality of first signals and said information signals to generate a respective plurality of intermediate frequency signals, the frequencies of said intermediate frequency signals being a predetermined difference between said first signals and the information signals;   sensing signal generating means responsive to said intermediate frequency signals for generating a sensing signal for each of said channels;   means for integrating said sensing signal; and   threshold means for generating a control signal to stop said first signal generating means by blocking the application of said train of first pulses to said first signal generating means in response to said first pulses and the integrated sensing signal whenever the sensing signal exceeds the threshold of said threshold means during the occurrence of one of said first pulses   whereby the sensing signals are normally discriminated from noise signals since the latter signals, when integrated, do not exceed said threshold during the occurrence of said first pulses.   
     
     
       2. A device as in claim 1 where said threshold means includes a logic gate responsive to said first pulses and the integrated sensing signal and a bistable storage device responsive to said logic gate for generating said control signal.